There are many varied forms and shapes of inserts being utilized in drill bits currently. One of the most common insert shapes utilizes a cylindrical base portion for insertion into the drilled opening or socket in the bit cutter, with the upper or protruding portion of the insert being substantially conical in shape. Many various shapes for the conical end of this insert are in use. Primarily, the truncated cone shape has the sharp edges rounded off and a relatively blunt tip remaining. Other variations utilize the truncated tip sharpened with opposed flats formed by cutting away a slice of the truncated cone on each side.
A second basic insert configuration as opposed to the cylindrical-frusto conical insert, is the cylindrical-hemispherical insert shape. This insert has a base portion which is cylindrical in nature and adapted to project into the cylindrical opening or socket in the cutter cone. The protruding portion of the insert is hemispherical-shaped. This insert is used substantially in drill bits for drilling hard formations.
The majority of drill bit inserts utilized in soft and medium formation bits comprise the cylindrical-frusto conical configuration with several variations of modification to the basic frusto conical protruding tip. Generally, these modifications previously consisted of "slabbing off" the opposing sides of the upper tip of the frusto conical section and a rounding off of the corners and sharper edges of the protruding end. The commonly termed chisel-shaped insert and the tooth-shaped insert essentially comprise a basic frusto conical shape with differing amounts of opposing sides "slabbed off". The result of such slabbing off is that the outer extending portion of the frusto-conical insert has a relatively long flat shape with a flat blunt outer end. This shape suffers from the disadvantage that the two outermost corners of the frusto-conical shape are subject to high stresses and therefore suffer rapid wear and/or early breakage. During the complex motion of the rolling cutters at the bottom of the well bore in the drilling operation, various portions of the insert are in contact with the formation being drilled at various points of rotation of the cutter on its lug. In many situations the first point of contact between the insert and the hard formation material occurs at one of the two flat projecting corners of the frusto conical shape. This oftentimes results in breakage of one of these corners or loosening of the insert in its cutter socket.
Another type of insert is a long, pointed, conical insert with hemispherical end and no flats. It is either too sharp and breaks easily or is too blunt and won't get good penetration in hard and medium-hard formations.
The present invention overcomes the difficulties of the frusto conical insert shape by utilizing a combination of cylindrical, conical, hemispherical and flat surface configurations in the insert design.